1. Field of the Invention
The present invention relates to semiconductor electronic devices, and, more particularly, to diode limiters.
2. Description of the Related Art
Microwave limiters are typically used in a microwave receiver as passive protection devices and are placed between an antenna and a mixer or low noise amplifier (LNA) to protect the mixer or LNA from burnout due to excessively large rf input to the antenna. The essential features of a limiter are small insertion loss at small-signal input levels to preserve the receiver noise figure and large insertion loss at large-signal input levels to protect the mixer or LNA. Conventional radar receivers use hybrid silicon p-i-n diode limiters in a passive mode; and to meet the required limiting and insertion loss specifications the hybrid silicon p-i-n diode chips used in these limiters are extremely small making them difficult to bond into circuits. The parasitic bond wire inductances used to bond the diodes into the circuit reduce the bandwidth over which the limiter maintains an acceptable small-signal match; see FIG. 1 for a schematic illustration of a silicon diode bonded into a hybrid microwave circuit. Note that silicon has inherently longer carrier storage times than gallium arsenide and, consequently, silicon p-i-n diodes have a lower on-resistance; but silicon is not appropriate material for monolithic microwave circuits due to high substrate losses and inability to incorporate into monolithic circuits.
More generally, the noise figure (NF) and gain requirements of galium arsenide LNAs are increasing in both military and commercial devices, and these requirements are usually met with ever decreasing MESFET gate lengths. However, decreasing gate length implies increasing sensitivity to electrostatic discharge and burnout. Thus a passive silicon diode limiter at the input of a LNA is typically used; but again the small size of silicon p-i-n diode chips makes for difficult bonding into hybrid microwave circuits and low yield for the hybrid device.
Thus known limiters have problems including lack of broadband small-signal match and low yield of hybrid devices.